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#2468243 - 03/18/18 05:22 PM Blown in Insulation - knob and tube wiring
Faust Offline
pro stock

Registered: 01/19/03
Posts: 1515
Loc: Massachusetts
I have a 1900 house which is still about 70% knob and tube wiring. I understand that this is the safest there is, arcing is almost impossible. I looked into blown in insulation and no one wanted to touch it with the knob and tube. Is this an excess of caution, or are there real issues.


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#2468248 - 03/18/18 05:28 PM Re: Blown in Insulation - knob and tube wiring [Re: Faust]
BIGGERED Offline
Reasonable Title

Registered: 04/17/06
Posts: 996
Loc: North East USA
I have never heard of knob and tube being "the safest thing there is"

The few I know who have encountered it make a point to remove it. May have been safe back in the day but I can not imagine the insulation is up to the task a hundred years after it was installed?

Red

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#2468255 - 03/18/18 05:37 PM Re: Blown in Insulation - knob and tube wiring [Re: Faust]
Alaskan_TA Offline
Fluffy Balladeer

Registered: 01/20/03
Posts: 26866
Loc: Moredoor, PA
My place is also about the same age. I tore all the old crap out.

Varmit chewed insulation, shop feed spliced into the 220 for the kitchen stove, it was scary.

Wiring first, then insulate as your budget allows.

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#2468256 - 03/18/18 05:37 PM Re: Blown in Insulation - knob and tube wiring [Re: Faust]
rapom Offline
top fuel

Registered: 01/21/03
Posts: 1721
Loc: Northern OH
My house has the remnants of tube and knob along side the new wiring. I lost count of all the scorch marks on the wood around some of the knobs. I always heard that tube and knob was a fire hazard and my house (1920) has lots of proof.


Attachments
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Edited by rapom (03/18/18 05:44 PM)

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#2468268 - 03/18/18 06:07 PM Re: Blown in Insulation - knob and tube wiring [Re: Faust]
RoadRunner Offline
master

Registered: 01/19/03
Posts: 4613
Loc: East Aurora (Buffalo) NY
For the current load old houses had, knob and tube wiring was probably pretty safe. Back then there were lights and maybe a few small appliances like a radio. Now days, I would not use the knob and tube wiring. Insulation will not allow any heated wires to cool down and could lead to a fire. We pulled all of ours out when we remodeled.
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#2468277 - 03/18/18 06:37 PM Re: Blown in Insulation - knob and tube wiring [Re: Faust]
Nukechargerboy Offline
super stock

Registered: 03/05/04
Posts: 792
Loc: Ossining, New York
I would call an electrician in before I proceed. pull new wire and sleep at night.

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#2468297 - 03/18/18 06:58 PM Re: Blown in Insulation - knob and tube wiring [Re: Faust]
Hemi_Joel Offline
master

Registered: 01/19/03
Posts: 5554
Loc: Minnesota
Back in 1981, I sprayed cellulose over the knob & tube wiring in the attic of a 1920 duplex I owned from '80 to '85. I can't say it was a good idea, but I drove past it last year and it is still standing.
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#2468421 - 03/18/18 11:08 PM Re: Blown in Insulation - knob and tube wiring [Re: Faust]
Faust Offline
pro stock

Registered: 01/19/03
Posts: 1515
Loc: Massachusetts
"the safest thing there is". I got that from my father who was an electrical engineer. His reasoning was that the wires were so far apart, they could never arc. None of the insulation guys had an explanation of why they wouldn't touch it.

Any way, ran into the Building Inspector at a coffee shop tonight. Local code doesn't allow it. The reasoning is this. The old wire can handle a pretty good load, so long as it is exposed to air for cooling. Any type of insulation (in the stud spaces) prevents it from cooling and reduces the load it can carry. Might also burn off the old fabric insulation on the wire. True, or not true, doesn't matter; it is code.

Reminds me of an old apartment house I have. When I gutted it, I found all of the electric switches were labeled "Thomas A. Edison Co."

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#2468423 - 03/18/18 11:17 PM Re: Blown in Insulation - knob and tube wiring [Re: RoadRunner]
yorker Offline
Village Idiot

Registered: 09/08/05
Posts: 1792
Loc: Walmart parking lot
y house still has most of it except where new circuits were installed. I think the people do not want to blow insulation over it in case for some reason there was any fire, they would not be named in a law suit.

the picture of the burned wood above may be from where they soldered the wiring when installed. Only issue I have seen with it is where it has been handled for new switches or receptacles, the wiring insulation breaks off. Also in my house, the ceiling light fixture boxes are 3/4 inch deep and old fixture wiring was made between the wood ceiling and fixture.
Any professional, just has to say it has to be removed for safety. Some insurance co.'s won't insure if present.
The installation just does not meet codes of last 50 years. Not grounded, no gfci or arc fault protection.

Not goinfg to remove mine.
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#2468451 - 03/19/18 01:38 AM Re: Blown in Insulation - knob and tube wiring [Re: Faust]
4mayhemi Offline
enthusiast

Registered: 11/28/16
Posts: 211
Loc: between the coasts
In all my years when coming across knob&tube, I have never met anyone wanting to keep it, just running away from it. I'll be darned, here in this thread there are 2!

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#2468576 - 03/19/18 11:51 AM Re: Blown in Insulation - knob and tube wiring [Re: Faust]
FM3_1970 Offline
master

Registered: 06/16/03
Posts: 5027
Loc: South Carolina
The building inspector is probably right about your local Code. When I looked into it a few years ago, it was allowable to insulate if the k & t was in a raceway but not directly over wires, so air gap was preserved. I think NEC might have been modified in some areas to allow for insulation, because fire risk not as high as once thought, but local Codes trump NEC. In theory, k & t is safer than other wiring (if done right), as your father suggests; however, older systems don't allow for modern loads, there's no way to ground things properly, and it's really easy to cowboy up a k & t system, so over the years all kinds of weird additions and unsafe splicing could have been done. Most Codes allow for installation of GFCI outlets with k & t, and so possible to use grounded plugs, but it's not as safe as modern grounded systems, obviously.
Last I checked. the NEC didn't actually prohibit k & t, and some Codes might allow for replacing old k & t with new k & t. I've heard of some guys installing it in new construction, but those guys are...eccentric, and I dunno if any Code actually allows it.

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#2468665 - 03/19/18 03:21 PM Re: Blown in Insulation - knob and tube wiring [Re: Faust]
RoadRunner Offline
master

Registered: 01/19/03
Posts: 4613
Loc: East Aurora (Buffalo) NY
On a side note, all high voltage transmission lines are basically knob and tube wiring.
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69 Road Runner w/472 Hemi & 4 speed.
70 Challenger R/T SE EF8 w/ V9J, U - A32 - Major Project

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#2468728 - 03/19/18 05:40 PM Re: Blown in Insulation - knob and tube wiring [Re: Faust]
cudaman1969 Offline
master

Registered: 01/25/04
Posts: 4335
Loc: fredericksburg,va
If exposed to see I would keep it, just for the looks, no power. Put up a sign that says "HIGH VOLTAGE" for laughs. Run the regular wire, hidden.

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#2468767 - 03/19/18 07:02 PM Re: Blown in Insulation - knob and tube wiring [Re: Faust]
SteveS Offline
top fuel

Registered: 02/26/06
Posts: 2257
Loc: Groveland, MA
I removed all of mine. The insulation was crispy in spots, and the wire itself broke easily if you had to change a switch or outlet. Then there is the lack of ground.

When my father bought the house, it had a 30 amp 110V service - only two wires coming in.
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#2468873 - 03/19/18 10:27 PM Re: Blown in Insulation - knob and tube wiring [Re: Faust]
5thAve Offline
master

Registered: 01/19/03
Posts: 2720
Loc: Posts: 4034 - Register...
On top of the insulation stopping the air cooling its also giving it one more thing to burn if it does heat up.
The biggest problems with knob and tube are more from the hacks that get to it over the years and age problems. The reason its so far apart is because the insulation sucked. Thats hardly a safety bonus.

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#2468901 - 03/20/18 12:03 AM Re: Blown in Insulation - knob and tube wiring [Re: Faust]
DAYCLONA Offline
I Live Here

Registered: 12/10/07
Posts: 15727
Loc: Mass
Originally Posted By Faust
"the safest thing there is".



Maybe back in the 30's when it was installed...

My house was built in 1870, the K&T probably got put in around the turn of the century, in fact some wasn't even K&T, some was highly decorative hand carved wooden strips with grooved channels that they laid the wire in along the baseboard, then nailed a hand carved ornate wooden strip cover over the wires...vintage, antique, historical or not, it's pure crap in today's world, you can't replace it fast enough

FYI: I do have blown in insulation, I estimate is was done in the 70's, and K&T was present in the walls with the insulation with no ill effects that I've seen, but for what little sleep I do get, I like to know I not going to wake up to a fire because of it, so although it's a pain in the [censored] fishing wires, take the time to run current code wiring....

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#2470359 - 03/22/18 11:43 AM Re: Blown in Insulation - knob and tube wiring [Re: Faust]
lockjaw-express Offline


Registered: 08/25/14
Posts: 463
Loc: Ohio
Knob and Tube wiring is not safe, and was never safe. You are asking for trouble with blown in insulation with K&T wiring. Bite the bullet and install 12/2 w/Ground, and that is good to 20 Amps of current load. Then do your blown-in insulation.

My 2 cents...

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#2470778 - 03/22/18 10:54 PM Re: Blown in Insulation - knob and tube wiring [Re: Faust]
Mr_fixit Offline
top fuel

Registered: 01/20/03
Posts: 1760
Loc: Rustylvania
knob and tube has to go, first.

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#2470787 - 03/22/18 11:22 PM Re: Blown in Insulation - knob and tube wiring [Re: Faust]
Mr. Smurf Offline
super stock

Registered: 03/08/07
Posts: 963
Loc: Mid Michigan
35 years ago, I was re-wiring knob & tube houses with my dad.

Scary stuff back then, can't imagine it now.

Hope you have damn good insurance.

Ed

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#2471042 - 03/23/18 03:56 PM Re: Blown in Insulation - knob and tube wiring [Re: Faust]
Hemi_Joel Offline
master

Registered: 01/19/03
Posts: 5554
Loc: Minnesota
Here is an interesting case for leaving the K&T:
http://www.homeenergy.org/show/article/nav/letters/page/10/id/1202
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